1. Field of the Invention
This invention relates to a method and apparatus for mixing and activating synthetic organic polymers at a relatively high rate in either batch or continuous loads and being able to control, select, alter or maintain the polymer concentration and activation.
The use of synthetic organic polyelectrolytes has grown rapidly over the past two decades. Only a few years ago, a U.S. Environmental Protection Agency listed only approximately 450 polymer products approved for use in potable water treatment systems. Today, over 1,000 synthetic polymer formations have been approved for use in potable water production and as many as 10,000 variations may exist in all liquid/solid separation applications worldwide, In classifying synthetic organic polymers commonly used in water treatment, it is important to consider charge type, product form and relative molecular weight. The charge may be anionic, cationic or nonionic. The polymer may be a dry powder, a solution (in water), or an emulsion. Relative molecular weights vary from low to very high. Unactivated or neat polymers are encased by an oil carrier. In this phase, a molecule is coiled upon itself. Due to its charge, and as it tries to uncoil the oil carrier overcomes the charge and keeps it coiled.
As appropriately stated in the article "Characterization of Synthetic Organic Polyelectrolytes Used in Water Treatment" by Beth M. Gucciardi and Dr. Steven K. Dentel, PhD, presented to the Chesapeake section of the American Water Works Association,
[A]s a general description, a polymer can be defined as a chemical compound made up of repeating structural units which are comprised mainly of carbon and hydrogen. The structural units, or monomers are linked together to form long chains in a process called polymerization. If the monomers are positively charged, the polymer is referred to as cationic. When the polymer is comprised of negatively charged units, it is termed anionic. If the net charge on the polymer is zero, it is described as nonionic. A typical cationic polymer contains positively charged nitrogen atoms on some or all of its repeating units. An anionic polymer may get its charge from negatively charged oxygen atoms. An anionic polymer can result from either equal combination of negative and positive units or from the absence of charge units along its chain. If a polymer is made up of only one type of repeating unit, or monomer, it is a homopolymer. If two types of monomer uniformly alternate along a polymer backbone, it is a copolymer. The number and type of repeating units comprising a polymer molecule determine its molecular weight. Since many monomer units are require to make up a polymer, these weights are high, ranging from ten thousand to ten million.
Liquid, or emulsion, polymers are dispersions of high solids synthetic polymer gels in hydrocarbon oil. The molecules in the gel are coiled and considered inactive and in their continuous phase. The advantage of supplying a polymer in its continuous oil carrier phase is primarily its ease of shipping and storage life. Polymers are highly polar due to the amide and carboxyl groups. This gives the polymer a great affinity for water but an aversion to oil. A polymer is considered inactive until blended with a good solvent such as water to initiate the hydration (activation) process.
Polymer gels are colloidal suspensions in which the dispersed synthetic polymer phase has combined with the continuous aqueous phase to produce a semi-solid material. Gels are also fluid-like colloidal systems consisting of long-chain, nitrogen-containing, macromolecules in a semi-solid form. Emulsions are dispersions of high-solids synthetic polymer gels in hydrocarbon oil. All solid synthetic polyelectrolytes result from differences in processing of polymers prepared in aqueous solutions, or in an aqueous phase of a suspension. The synthesis results in a rigid, tough, rubber gel. Processing the tacky gel particles, with heat, produces the "dry" or "powder" solid polyelectrolyte product.
Liquid polymers are used by industry to simplify their industrial processes and make them more economical. For example, liquid polymers may be used for water purification and flocculation; may be used in automotive paint spray booths to detackify paint; may be used in the chemical industry to separate inorganics and other solids from plant effluent; may be used in the coal industry to promote solids settling and recover fine coal; may be used in the petroleum industry to enhance oil recovery; may be used in the phosphate industry to process tailings; may be used in the pulp and paper industry as retention and dewatering aids; and may be used in the steel industry to settle wastes. Those familiar with this technology and art will readily perceive many more uses in still other industries.
Polymers in liquid form are normally supplied in 5 gallon containers, 55 gallon lined drums, 350 gallon portable bin containers, 5,000 gallon tank trucks, and 10,000 to 30,000 gallon railroad tank cars. Usually emulsion polymers are shipped in their continuous phase (nonactivated) to the location where they will be used. At that location, it is necessary to activate the polymers. Usually that means that a polymer must be inverted in an electrolyte solution, usually water, to its discontinuous phase (active). The process for so converting the polymer into an active state is one of imparting a sufficient amount of energy to the polymer.
The exact amount of energy required for the activation of an emulsion polymer is factor dependent. Variations in molecular weight, solution concentration, water constituents, and percent active solids may affect she amount of energy needed to properly invert the polymer. When the polymer has been inverted, there is likely to be an increase in viscosity of the polymer solution. The increase in viscosity is due to the extended molecules entirtwining with each other. With the polymer molecule extended, polymer-polymer entanglements can be maximized.
2. Description of the Related Art
As noted above, the process for activating polymer requires a sufficient amount of energy on the polymer in order to break and disperse the polymer gel and allow the molecules to extend. Reference may be made to U.S. Pat. No. 4,057,223 issued to Mr. Roy R. Rosenberger and U.S. Pat. No. 4,217,145 issued to Mr. Preston G. Gaddis for examples of prior art polymer activating systems.
The polymer gel encased in the hydrocarbon carrier is inactive, and therefore, its hydrocarbon barrier must be neutralized to allow contact between the electrolyte, solutes and cosolutes and thus allow the ionic molecule to hydrate. The way in which emulsion polymers are activated includes diluting them with a solvent (water) and adding enough mixing energy to emulsify the oil carrier and enable the ionic charge molecule to uncoil. More particularly, the energy imparted to the inactive polymer includes a mechanical agitation which breaks down the lipid barrier and thus enables water or another electrolyte to reach the long coiled molecule. Once that molecule is in water, the repulsive interactions between the fixed charges on the polymer chains uncoil the molecule to expose its reactive sites. Until this uncoiling occurs, the molecule is useless for most purposes.
The known activation systems have required relatively long periods of time, up to and even over an hour, in order to complete the activation of the polymer. In order to satisfy the time requirements often prior art systems utilize aging or auxiliary retention chambers where the activated polymer is allowed to sit while the molecules untangle and extend. This additional period of time increases the requirements and capacities for holding and aging tanks during activation. Therefore, the relatively long activation time can become very expensive. Also, the requirements for such a long term for activation greatly increases capital requirements for the purchase of machinery when a system is operating continuously. Thus, a faster, more efficient activation system is highly desired.
Primarily, the prior art used the batch method to activate liquid polymers. Polymer and water are delivered to a common mixing tank. Once in the tank, the solution is beat or mixed for a specific length of time in order to impart energy thereto. After mixing, the resulting solution must age to allow enough time for the molecules to unwind. This method, due to its inefficient mixing and localized shear planes, did not necessarily yield the highest quality polymer solution.
Other prior art shows continuous in-line mixers as well as in-line static mixers. Standard mixers utilized for mixing and feeding are shown in U.S. Pat. Nos. 4,522,502 and 4,642,222 issued to Carl Brazeitoh, as well as U.S. Pat. No. 4,747,691 issued to Robert O. Hoffland. Examples of prior art static mixers can be found in U.S. Pat. No. 4,051,065 issued to Gerard J. Venema, as well as U.S. Pat. No. 3,067,987 issued to Sidney R. Ballou, et el.
Accordingly, one purpose of this invention is to provide a new and improved means and methods for activating polymers. In particular, to provide a quicker, multi-stage procedure which lends itself to the either batch or continuous processing and provides a means of structuring the polymer molecule to yield higher levels of activated product.
Another object of this invention is to provide a means for activating polymers which provides an inexpensive way to enhance the productivity of systems currently in place. Consequently, it is an object of the present invention to provide an automatic, continuous system which is able to vary the output rate of inverted polymer, while automatically maintaining the amount of energy imparted thereto and a desired concentration of the polymer in a quick, efficient and relatively inexpensive manner.
Still another object of the present invention is to substantially reduce, and in many cases completely eliminate, the aging time which in turn reduces the capital expenditures required to install a polymer mixing and activation system.